Field of the Disclosure
The present disclosure, for example, relates to wireless communication systems, and more particularly to techniques for managing handovers in an unlicensed radio frequency spectrum band.
Description of Related Art
Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, single-carrier frequency-division multiple access (SC-FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
By way of example, a wireless multiple-access communication system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, otherwise known as user equipments (UEs). A base station may communicate with UEs on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station).
Some modes of communication may enable communications between a base station and a UE over an unlicensed or shared radio frequency spectrum band, or over different radio frequency spectrum bands (e.g., a licensed radio frequency spectrum band or an unlicensed radio frequency spectrum band) of a cellular network. With increasing data traffic in cellular networks that use a licensed radio frequency spectrum band, offloading of at least some data traffic to an unlicensed or unlicensed radio frequency spectrum band may provide a cellular operator with opportunities for enhanced data transmission capacity. An unlicensed radio frequency spectrum band may also provide service in areas where access to a licensed radio frequency spectrum band is unavailable.
Prior to gaining access to, and communicating over, an unlicensed radio frequency spectrum band, a base station or UE may perform a listen before talk (LBT) procedure to contend for access to the unlicensed radio frequency spectrum band. An LBT procedure may include performing a clear channel assessment (CCA) procedure to determine whether a channel of the unlicensed radio frequency spectrum band is available. When it is determined that the channel of the unlicensed radio frequency spectrum band is available, a channel usage beacon signal (CUBS) may be transmitted to reserve the channel.
In some modes of operation, a UE and a serving base station may operate using an unlicensed radio frequency spectrum band in which the serving base station may not detect one or more other transmitting device that may transmit using the unlicensed radio frequency spectrum band. For example, the serving base station may transmit using the unlicensed radio frequency spectrum band in a time division multiplexing manner with another base station which may result in the serving base station transmitting at the same time as the other device(s) and not detecting the signals of the other device(s). In other examples, the other device(s) may be outside of an energy detection range of the serving base station, but close enough to the UE to cause interference. In such cases, it may be desirable to serve the UE through a different base station.